The Menai Strait is a place of beauty, inspiration and respect. It also
plays an important role in the history of Wales, from the last defence
of the Druids against the invading Roman army, to the present day.

Tidal Race

The eminent geologist Edward Greenly wrote of the Menai Strait in 1919
"Few valleys in Britain have been more discussed than the Menai Strait."
The 15 miles of river-like channel, overhung by quiet inland woods, yet
fringed along their shores with seaweed; the clear waters twice a
day placid like a lake, yet twice a day moving in a tide-race that
can be heard a mile away; these things a sort of paradox of Nature,
that cannot but rouse the scientific imagination to inquiry." He
would no doubt be pleased that the entire length of the Menai Strait has
been proposed as a Marine Nature Reserve. Indeed, if all goes well,
it will become one soon. Recently a revised consultative document
was published by the Countryside Council for Wales who are responsible
for designating and looking after Marine reserves in Wales. The document
explained the rationale behind designation and what could be achieved once
it had taken place. The Menai Strait will be only the second Marine Nature
Reserve in Wales and only the third in the whole of England and Wales.

Morphology

The Menai Strait is a narrow, 25 km long, strip of sea-water separating
the Island of Anglesey from mainland Gwynedd. It consists of two
parallel, but separate, reaches which trend roughly north-east to south-west,
separated by a narrow middle reach which trends roughly north-south.
The narrow southern end (Fort Belan across to Aber Menai Point) is
only 400 metres wide at high tide. From here it widens to a maximum
of 1100 metres across from Traeth Gwyllt to Caernarfon Castle, and then
narrows again until the middle reaches (Port Dinorwic and Menai Bridge)
where it is only about 500 metres across. After this it broadens
again until, at Bangor Pier, it is 900 metres wide, whilst the distance
Puffin Island to Penmaenmawr is some 7.5 km in length.

The Straits has many regions with outcrops and rocky areas, however,
most of it is composed of shallow intertidal mudflats and sand banks, such
as Traeth Lafan and Traeth Melynog. There are also a number of deep
hollows, e.g. at Pwll Fanogl, where there is one that is about 25
metres in depth. This particular hollow is thought to result from
the formation of a pothole at a time when a local river discharged to this
area at the end of the last ice age.

Geology and Geomorphology

The rocks that form the shore of the Menai Strait span about 600
million years. The geology is complex and includes rocks from
the Pre-Cambrian Mona Complex, Cambrian Sandstone, Ordovician and Silurian
shales, Carboniferous sedimentary deposits, Palaeozoic igneous intrusions
and recent rocks of marine alluvium. About 85% of the Menai
Strait is underlain by a variety of unconsolidated deposits.
These are predominantly Quaternary sediments with a venire of more recent
sands, muds, shingle and boulder.

At the end of the last glaciation the Menai Strait lay beneath the meeting
point of ice of North Wales origin and that from the north (Irish Sea Ice).
As a result it was moulded, in impart, by the action of both ice and melt
water drainage. As sea levels rose at the end of this period the
Menai Strait was submerged and features such as Aber Menai point were formed.

WHAT IS SPECIAL ABOUT THE MENAI
STRAIT?

The Menai Strait was chosen as a potential Marine Nature Reserve for
a variety of reasons. It was first studied at end of the last century
when Liverpool University set up a Marine Station on Puffin Island.
Once diving opened the underwater world the diversity of life became clear.
The biology of the Swellies in particular is both rich and diverse, due
to its unique combination of environmental factors. It would in itself
be worth preserving, but when combined with the complex and valuable geological,
geomorphological and hydrographical features, the area is outstanding.

Water flow, tides and currents:

The biological interest of the Strait is dependent upon the tidally
driven water flows. Though the overall movement of water is towards the
south-west the actual tidal pattern is complex. The inflowing
tide enters the Strait at Abermenai Point and from here it flows northward.
However, before it can reach the other end of the Strait, the tidal wave
(which travels faster in deeper water) has passed around Anglesey and entered
the Strait for a second time at the Bangor end. This results in the
two opposing flows meeting somewhere between the Swellies and Bangor
pier, with the actual point of meeting dependant on wind and
tidal conditions. These tides generate strong currents that can reach a
maximum of 8 knots in some locations. Despite its proximity to land, and
the freshwater input of small rivers such as the Ogwen and Seiont, salinities
within the Strait are near to those of the open sea (generally in excess
of 3.0%, the water of the Irish Sea is about 3.4%). These high salinities
allow a much greater diversity of marine life than is found in more estuarine
environments.

Biology:

The Menai Strait has a wide variety of habitat types and is home to
over 1,400 recorded species of plants and animals. Although we know
of no species that are unique to the Menai Strait the combination of strong
currents and other environmental factors has led to the development of
a number of rare features and unusual animal associations. For example,
Halichondria
panicea (a sponge) and Tubularia indivisa (a hydroid)
live together, forming extensive mats over the sea bed in the area of tidal
rapids. It is these very currents which both supply food and prevent
the deposit of sediment.

The Strait is also inhabited by a number of rare creatures.
These include the brachiopod Gwynia capusla, which lives
between sand grains, and the rock boring Little Piddock,
Barnae
parva. Whilst restricted to the west of Britain in the Strait
it bores into the blocks of limestone which make up the Menai Suspension
Bridge!

Various shellfish are also found Lobsters, once common are now
both smaller and harder to find. Mussels are grown commercially to
the north and at Tal-y-foel. Cockles are found in considerable number
at Traeth Lafan and Traeth Melynog.
However, recent work at Traeth Lafan showed that if they are collected
by hydraulic dredging there is a considerable reduction in the pre-market
sized 1 year olds and that other types of none commercial bivalve are also
damaged. Ragworm, of an unusually large size, are traditionally found
in the more muddy areas of the shore. Unfortunately, both locals
and visitors dig them for bait. Superficially, this only appears
to cause temporary disturbance, however, recent studies indicate both that
some of the stocks overexploited, and that the act of digging is extremely
destructive of habitat.

Common
Cockles

The Strait is also home to internationally important numbers of birds,
and Traeth Lafan is designated as a Special Protection Area under the EC
Birds Directive. The large number and variety of waders feed on the
many marine invertebrates and rely on the area both as a refuelling stop
on their autumn and spring migrations and as a refuge in winter.
Larger animals, such as Seals and Porpoises, use
the Menai Strait as a short cut from Caernarfon Bay to Liverpool Bay, and
Otters
are occasionally seen on the shore or in the water.

Archaeology:

The remains of Goradau (fish traps) are found along the shore.
One, at Menai Bridge, dates from as early as the 14th century, but the
best preserved is at Ynys Gorad Goch. This was built, complete with
the fish smoking chamber, in 1824, and was used continuously until 1959.

The Strait has always been heavily used by shipping and inevitably
a number of these vessels have come to grief. One of the best studied
is the Pwll Fanogl slate wreck. This, a clinker built vessel made
of 'western oak', is thought to have sunk between 1570 and 1690.
Today it is one of only three Welsh wrecks protected under the 'Protection
of Wrecks' Act 1975.

Recreation and Education

The Menai Strait supports a wide variety of recreational activities
ranging from sailing to fishing and bird watching.
It is also a local feature attracting many tourists who walk in and admire
the landscape of this region.

Due to its diversity the Menai Strait is regularly used by schools,
colleges and universities for the 'in field' teaching and training of subjects
such as marine biology, geology and geomorphology.

Conservation and the value of a Marine
Nature Reserve

Considerable anxiety has been expressed as to the state of the Menai
Strait. It is thought to be suffering increased disturbance and pollution.

A steady reduction in water clarity has been recorded since the 1970's
and with it a decline in certain species of sponge. Seaweed distribution,
especially foliose red algae has also changed because light can no longer
penetrate as far. This means that the plants can only thrive in shallow
areas, not in deeper ones where they were once common.

Today there are seven 'Sites of Special Scientific Interest' (SSSI)
and one National Nature Reserve adjoining the Menai Strait. Designation
of the entire stretch of the Menai Strait as a Marine Nature Reserve will
allow the conservation and maintenance of a unique ecosystem, as well as
promoting survey and research programmes into the area and enhancing its
educational and amenity value.

This article was previously published in welsh in the journal Dan
Haul
and in the Vernal 1995 issue of Glaucus.